What must be in a subnet addressing scheme?

Kenrick

Hi Network Experts,
I have answered some of the following questions but I don’t know what must be in a subnet addressing scheme, please guide me and correct me if I am wrong,thanks.

An organization is granted a block of IPv4 Class B address 150.85.0.0. The administrator wants to create 28 subnets.

(i)Analyse and design an appropriate subnet addressing scheme.

(ii) State a suitable subnet mask.
ans:11111111.11111111.11111000.00000000
(iii) Compute the number of hosts in each subnet. Exclude network (all 0s) and broadcast (all 1s) addresses.
ans:2046

(iv) Compute the range of subnet addresses. Exclude all 0s and all 1s subnet addresses.
ans:150.85.8.0-150.85.240.0